TiNb系亚稳β钛合金α"及ω相变的表面效应研究

Because of the importance of α" martensite and ω phase for the functional performance and mechanical properties of metastable β titanium alloys, the formation and their evoluation of α" and ω phases as well the relationship between their transformation and the mechanical behavior have been key issues in the fields of advanced titanium alloys and in solid physics. It was found in recent experimental study that during the quenching of metastable β titanium alloys，substancial surface effect of α" martensitic transformation and ω precipitation occurred，i.e. α" martensitic transformation only take place on the surface and a close correlation exists between the formation of α" and ω phases. It is of academic significance and technical importance to clarify the mechanism for the surface effect of α" martensitic transformation and correlation between the formation of α" and ω phases, which will deepen the study of martensitic transformation in metastable β Ti alloys. The aim of the present study is to clarify the influence of the structural stability, cooling rate and surface stress on the surface effect of α" and ω phase transformation, and to determine the physical mechanism of surface effect and the relationship between α" and ω phase transformation. In addition, single β phase Ti alloys with different strcutual stability will be prepared and the relationship between structual stability and deformation behavior will be investigated, in attempt to discover the origin for the relation of martensitic transformation and mechanical behavior, laying a basis for the design and development of advanced metastable β Ti alloys.

鉴于α"马氏体和ω相对亚稳β钛合金功能特性及力学性能的重要作用，α"及ω相的形成、演化及其与力学行为的关系一直是先进钛合金和固体物理领域的关键科学问题。我们近期的实验研究表明，亚稳β钛合金的α"马氏体相变及ω相变具有显著的表面效应，α"马氏体相变只发生在合金表层而非内部，同时α"相形成与ω相析出具有高度相关性。阐明该表面效应的物理机制以及α"相变与ω相变的相关性，将深化亚稳β钛合金中的固态相变学术研究。本项目拟以TiNb系亚稳β钛合金为对象，深入研究合金的结构稳定性、冷却速率和表面应力等因素对α"及ω相变表面效应的影响规律，阐明表面效应的物理机制以及α"相变与ω相变的相关性；利用α"马氏体相变的表面效应，制备具有不同稳定性的单一β相亚稳β钛合金，分析表征结构稳定性与力学行为的关系，揭示应力诱发α"马氏体相变与合金力学行为的相互作用机制，为新型亚稳β钛合金的设计和研发提供技术支持。

亚稳β钛合金是当前先进钛合金和和生物医用材料的前沿领域，深入理解合金的结构稳定性与力学行为的关系，对高性能亚稳β钛合金的设计研发具有重要的工程意义。本项目依据研究计划，全面完成了项目提出的研究内容，并取得了具有较高学术价值的研究成果。制备了具有不同β稳定性的TiNb 系(TiNb、TiNbZr 和TiNbSn)亚稳β钛合金，通过深入研究结构稳定性对相变表面效应的影响，建立了合金的 α″ 马氏体相变与ω相变之间的相互作用关系；结合亚稳β钛合金马氏体热力学和动力学，探讨了 α″ 马氏体相变及ω相变表面效应与合金β稳定性和冷却速率的关系，阐明了应力作用对 α″ 及ω相变表面效应及其演化的影响，揭示了亚稳β钛合金 α″ 马氏体相变表面效应的物理机制；通过研究结构稳定性与 α″ 马氏体相变及力学行为的关联性，揭示了Ti-Nb系亚稳β钛合金呈现超低弹性模量的物理机制，即：该类合金的超低弹性模量与该类合金反常低的剪切模量C44有关，从而阐明了亚稳β钛合金马氏体相变表面效应及力学行为(超低弹性模量)的机理。本项目的研究结果深化了亚稳β钛合金的固态相变研究，有助于理解亚稳β钛合金结构稳定性与力学行为的关系，对新型亚稳β钛合金的设计和研发具有参考价值。